Toner, toner accommodating container, developer, developing device, process cartridge, image forming apparatus, and image forming method

ABSTRACT

A toner comprising base particles and external additive particles covering the base particles is provided. The base particles comprise a binder resin and a colorant. The external additive particles comprise at least one member selected from the group consisting of fluorine-containing aluminum hydroxide, fluorine-containing boehmite, and fluorine-containing pseudoboehmite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application No. 2019-136594, filed onJul. 25, 2019, in the Japan Patent Office, the entire disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to a toner, a toner accommodatingcontainer, a developer, a developing device, a process cartridge, animage forming apparatus, and an image forming method.

Description of the Related Art

An electrophotographic image forming method includes a charging process,an irradiating process, a developing process, a transfer process, and afixing process. The charging process is for applying an electric charge,by electrical discharge, to a surface of a photoconductor serving as animage bearer. The irradiating process is for irradiating the chargedsurface of the photoconductor to form an electrostatic latent image. Thedeveloping process is for supplying toner to the electrostatic latentimage formed on the surface of the photoconductor to develop theelectrostatic latent image into a toner image. The transfer process isfor transferring the toner image formed on the surface of thephotoconductor onto a recording medium. The fixing process is for fixingthe toner image on the recording medium.

It has been difficult to simultaneously reduce wear of thephotoconductor and prevent generation of fog images over time inlow-temperature low-humidity environments by these techniques.

SUMMARY

In accordance with some embodiment of the present invention, a tonercomprising base particles and external additive particles covering thebase particles is provided. The base particles comprise a binder resinand a colorant. The external additive particles comprise at least onemember selected from the group consisting of fluorine-containingaluminum hydroxide, fluorine-containing boehmite, andfluorine-containing pseudoboehmite.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram showing a characteristic spectrum of a binder resinof a toner according to an embodiment of the present invention, obtainedby an FTIR-ATR (Fourier Transform Infrared Spectrometry-Attenuated TotalReflection) method;

FIG. 2 is a schematic view of a process cartridge according to anembodiment of the present invention;

FIG. 3 is a schematic view of an image forming apparatus according to anembodiment of the present invention;

FIG. 4 is a enlarged schematic view of a main part of FIG. 3;

FIG. 5 is a schematic view of an image forming apparatus according to anembodiment of the present invention, having a charger that performsroller charging; and

FIG. 6 is a schematic view of an image forming apparatus according to anembodiment of the present invention, having a charger that performsbrush charging.

The accompanying drawings are intended to depict example embodiments ofthe present invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“includes” and/or “including”, when used in this specification, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Embodiments of the present invention are described in detail below withreference to accompanying drawings. In describing embodimentsillustrated in the drawings, specific terminology is employed for thesake of clarity. However, the disclosure of this patent specification isnot intended to be limited to the specific terminology so selected, andit is to be understood that each specific element includes all technicalequivalents that have a similar function, operate in a similar manner,and achieve a similar result.

For the sake of simplicity, the same reference number will be given toidentical constituent elements such as parts and materials having thesame functions and redundant descriptions thereof omitted unlessotherwise stated.

In accordance with some embodiments of the present invention, a toner isprovided that is capable of producing high-density images while reducingwear of the surface of an electrostatic latent image bearer andpreventing generation of fog images over time in low-temperaturelow-humidity environments.

A toner according to an embodiment of the present invention comprisesbase particles and external additive particles covering the baseparticles. The base particles comprise a binder resin and a colorant.The external additive particles comprise at least one member selectedfrom the group consisting of fluorine-containing aluminum hydroxide,fluorine-containing boehmite, and fluorine-containing pseudoboehmite.

Heretofore, no technique has been known to use, as external additiveparticles, aluminum hydroxide, boehmite, and pseudoboehmite that aretreated with fluorine. The use of fluorine-treated alumina as anexternal additive has been proposed. However, fluorine-treated aluminahas drawbacks that the charge level is low and fog images are generated.Further, it is also difficult to prevent wear of an electrostatic latentimage bearer (hereinafter also referred to as “photoconductor”) when thefluorine-treated alumina is used as external additives.

In view of this situation, in the present disclosure, at least oneselected from fluorine-containing aluminum hydroxide,fluorine-containing boehmite, and fluorine-containing pseudoboehmite isused as external additive particles. Such external additive particlesprovide a toner capable of producing high-density images while reducingwear of the surface of the photoconductor and preventing generation offog images over time in low-temperature low-humidity environments.

External Additive Particles

In the present disclosure, the external additive particles comprise atleast one selected from fluorine-containing aluminum hydroxide,fluorine-containing boehmite, and fluorine-containing pseudoboehmite.The external additive particles may further comprise particles otherthan the above (hereinafter “other particles”), if necessary.

Examples of the aluminum hydroxide include, but are not limited to,amorphous aluminum hydroxide and bayerite.

Boehmite and pseudoboehmite are known and can be synthesized byconventional methods.

Incorporation of fluorine into aluminum oxide, boehmite, andpseudoboehmite can be performed by, for example, bringing thesecompounds into contact with a fluorine compound under heat. Examples ofthe fluorine compound include, but are not limited to,fluorine-containing silane coupling agents. Specific examples of thefluorine-containing silane coupling agents include, but are not limitedto, silane compounds in which a hydrogen atom of an alkyl group isreplaced with a fluorine atom, such as C₈F₁₇CH₂CH₂Si(OCH₃)₃,C₆F₁₃CH₂CH₂Si(OCH₃)₃, and CF₃CH₂CH₂Si(OCH₃)₃.

Other Particles

The other particles may be appropriately selected to suit to aparticular application. Examples thereof include, but are not limitedto, silica, titanium oxide, barium titanate, magnesium titanate, calciumtitanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tinoxide, quartz sand, clay, mica, sand-lime, diatomaceous earth, chromiumoxide, cerium oxide, red iron oxide, antimony trioxide, magnesium oxide,zirconium oxide, barium sulfate, barium carbonate, calcium carbonate,silicon carbide, and silicon nitride. Each of these can be used alone orin combination with others.

The other particles may be subjected to a surface treatment for thepurpose of increasing hydrophobicity of the surface and preventingdeterioration of fluidity and chargeability even under high humidity.

Specific examples of the surface treatment agent include, but are notlimited to, fluorine-containing silane coupling agents, silylationagents, silane coupling agents having a fluorinated alkyl group, organictitanate coupling agents, aluminum coupling agents, silicone oils, andmodified silicone oils.

The amount of the at least one selected from fluorine-containingaluminum hydroxide, fluorine-containing boehmite, andfluorine-containing pseudoboehmite is preferably from 0.5 to 2.0 partsby mass, more preferably from 1.0 to 1.5 parts by mass, based on 100parts by mass of the base particles (to be described in detail later).

When the amount is 0.5 parts by mass or more, the saturated charge valueof the toner in a low-temperature low-humidity environment (for example,at a temperature of 10 degrees C. and a relative humidity of 15%) isincreased, and high-density images are provided. When the amount is 2.0parts by mass or less, fluorine derived from the external additiveparticles is prevented from adhering to carrier particles over time. Asa result, the charging ability of the carrier is increased, the chargerising property of the toner in a low-temperature low-humidityenvironment is improved, the number of weakly-charged,excessively-charged, and reversely-charged toner particles is reduced,and generation of fog images is prevented. Further, wear of thephotoconductor is reduced.

In the present disclosure, the external additive particles have aparticle diameter (D50) of preferably from 8 to 120 nm. With thisparticle diameter, the toner is less prone to fluctuate in propertiessuch as charge amount, fluidity, and cohesion, and is prevented fromdegrading image quality (by, for example, causing transfer failure orgenerating background stains). When the particle diameter is 120 nm orless, wear of the photoconductor is reduced.

More preferably, the external additive particles have a particlediameter (D50) of from 12 to 60 nm.

The particle diameter (D50) of the external additive particles can bemeasured by a laser diffraction particle size distribution analyzerLA-750 (manufactured by HORIBA, Ltd.).

According to the study by the inventors of the present invention, it hasbeen found that, to improve the charge rising property that is anability of toner to be charged in a short time upon friction with acarrier whose charging ability has deteriorated with time, there is asuitable relation between the aluminum density and the fluorine densityin the surface layer of the toner particle, particularly in a regionextending from the outermost surface layer of the toner particle to adepth of about 5 nm.

The toner according to an embodiment of the present invention satisfiesthe following formula (1), where X1 and X2 represent an aluminum densityand a fluorine density, respectively, as determined by X-rayphotoelectron spectroscopy (XPS).

2.7≤X1/X2 (atomic percent)≤5.8  Formula (1)

When the ratio (X1/X2) of the aluminum density X1 to the fluorinedensity X2 is 2.7 or more, fluorine derived from the external additiveparticles is prevented from adhering to carrier particles over time. Asa result, the charging ability of the carrier is increased, the chargerising property of the toner in a low-temperature low-humidityenvironment (for example, at a temperature of 10 degrees C. and arelative humidity of 15%) is improved, the number of weakly-charged,excessively-charged, and reversely-charged toner particles is reduced,and generation of fog images is prevented. When the ratio (X1/X2) is 5.8or less, the fluorine density that contributes to the charge risingproperty of the toner is appropriate. As a result, the charge risingproperty of the toner in a low-temperature low-humidity environment isimproved, the number of weakly-charged, excessively-charged, andreversely-charged toner particles is reduced, and generation of fogimages is prevented.

When the aluminum density X1 is 2.1 or more, the saturated charge valueof the toner in a low-temperature low-humidity environment (at atemperature of 10 degrees C. and a relative humidity of 15%) becomesappropriate, and high-density images are provided. When the aluminumdensity X1 is 3.0 or less, fluorine derived from the external additiveparticles is prevented from adhering to carrier particles over time. Asa result, the charging ability of the carrier is increased, the chargerising property of the toner in a low-temperature low-humidityenvironment is improved, the number of weakly-charged,excessively-charged, and reversely-charged toner particles is reduced,and generation of fog images is prevented.

The aluminum density X1, the fluorine density X2, and the ratio X1/X2 ofthe toner can be measured by X-ray photoelectron spectroscopy (XPS)using the below-described instruments under the below-describedmeasurement conditions.

-   -   Analysis equipment: AXIS-ULTRA (manufactured by Shimadzu        Corporation)    -   X-ray: 15 kV, 9 mA, Hybrid    -   Neutralization gun: 2.0 A (F-Current), 1.3 V (F-Bias), 1.8 V        (C-Balance)    -   Step: 0.1 eV (Narrow), 2.0 eV (Wide)    -   Pass E: 20 eV (Narrow), 160 eV (Wide)    -   Relative sensitivity coefficient: Use the relative sensitivity        coefficient of Casa XPS

Preferably, the toner according to an embodiment of the presentinvention further contains a releasing agent, and satisfies the formula0.05≤W/R≤0.14, where W and R represent heights of peaks specific to therelease agent and the binder resin, respectively, measured by anattenuated total reflection method (“ATR method”) using a Fouriertransform infrared spectrometer (“FT-IR”).

When the ratio (W/R) is 0.05 or more, the release agent (wax) is presentin an appropriate region of the outermost surface layer of the toner. Asa result, even the toner is under stress caused by stirring in an imageforming apparatus, the external additive particles are prevented fromreleasing from the toner base particles. Furthermore, adhesion offluorine to the carrier is prevented, and generation of fog imagescaused due to insufficient triboelectric charge rising between the tonerand the carrier is prevented over time. When the ratio (W/R) is 0.14 orless, the release agent (wax) is present in an appropriate region of theoutermost surface layer of the toner. As a result, even the toner isunder stress caused by stirring in an image forming apparatus, embedmentof colorants in the toner base particles is prevented, and a decrease ofimage density and generation of fog images are prevented over time.

Measurement of Peak Intensity Ratio (W/R)

In the present disclosure, the ratio (W/R) is determined from anabsorbance spectrum obtained by an ATR method (total reflection method)using an FT-IR (Fourier transform infrared spectrophotometer AVATAR 370manufactured by Thermo Electron Corporation), in which the heights ofpeaks specific to the release agent (wax) and the binder resin,respectively, are defined as W and R. Since the ATR method requires asmooth surface, the toner is pressure-molded to form a smooth surface.Specifically, 2.0 g of toner is pressure-molded with a load of 1 t for60 seconds and formed into a pellet having a diameter of 20 mm.

In the present disclosure, the maximum height of a peak specific to C—Hstretching of an alkyl chain of the wax (e.g., a peak observed at 2834to 2862 cm⁻¹) is defined as W, and the maximum height of a peak specificto the binder resin (e.g., a peak observed at 784 to 889 cm⁻¹ for apolyester resin (see FIG. 1), a peak observed at 670 to 714 cm⁻¹ for astyrene-acrylic resin) is defined as R, and W/R is calculated as thepeak intensity ratio. When the binder resin is a mixture of two or moretypes of resins and two or more peaks are detected, the highest peak isadopted. In the present disclosure, the spectrum is converted so thatthe height of peak indicates absorbance. The peak intensity ratio iscalculated using absorbance values that indicate the height of peak.

Toner Base Particles

The toner base particles contain a binder resin and a colorant,preferably further contain a release agent, and may optionally containother components as necessary.

Release Agent

The release agent is not particularly limited and can be suitablyselected to suit to a particular application. Examples thereof include,but are not limited to, waxes.

Examples of the waxes include, but are not limited to: plant waxes suchas carnauba wax, cotton wax, sumac wax, and rice wax; animal waxes suchas beeswax and lanolin; mineral waxes such as ozokerite and ceresin; andpetroleum waxes such as paraffin, microcrystalline, and petrolatum.

In addition to these natural waxes, synthetic hydrocarbon waxes (e.g.,Fischer-Tropsch wax, polyethylene, polypropylene) and synthetic waxes(e.g., ester, ketone, ether) may also be used.

Examples of the waxes further include: fatty acid amide compounds suchas 12-hydroxystearic acid amide, stearic acid amide, phthalic anhydrideimide, and chlorinated hydrocarbon; homopolymers and copolymers ofpolyacrylates (e.g., poly-n-stearyl methacrylate, poly-n-laurylmethacrylate), which are low-molecular-weight crystalline polymers, suchas copolymer of n-stearyl acrylate and ethyl methacrylate; andcrystalline polymers having a long alkyl side chain.

Each of these release agents may be used alone or in combination withothers.

Among these, carnauba wax, rice wax, ester wax, and polypropylene arepreferred.

Carnauba wax is a natural wax obtained from the leaves of carnauba palm.Those with a low acid value from which free fatty acids have beeneliminated are preferred because they can be uniformly dispersed in thebinder resin.

Rice wax is a natural wax obtained by purifying crude wax produced in adewaxing or wintering process in purifying rice bran oil extracted fromrice bran.

An ester wax is synthesized by an esterification reaction between amonofunctional straight-chain fatty acid and a monofunctionalstraight-chain alcohol.

The amount of the release agent in the toner is not particularly limitedand can be suitably selected to suit to a particular application.Preferably, the amount of the release agent in 100 parts by mass of thetoner is from 0.5 to 20 parts by mass, more preferably from 2 to 10parts by mass.

When the amount is 0.5 parts by mass or more, the toner exhibitsexcellent high-temperature offset resistance and low-temperaturefixability when being fixed. When the amount is 20 parts by mass orless, heat-resistant storage stability is excellent, and high-qualityimages are provided. When the amount is within the preferred range,image quality and fixing stability are advantageously improved.

Binder Resin

Examples of the binder resin include: resins obtained by a condensationpolymerization reaction, such as polyester, polyamide, andpolyester-polyamide resin; and resins obtained by an additionpolymerization reaction, such as styrene-acrylic and styrene-butadiene.The binder resin is not particularly limited as long as it is a resinobtained by a condensation polymerization reaction or an additionpolymerization reaction.

A polyester resin obtained by a condensation polymerization reaction isa resin obtained by a condensation polymerization between a polyhydroxycompound and a polybasic acid.

Examples of the polyhydroxy compound include, but are not limited to:glycols such as ethylene glycol, diethylene glycol, triethylene glycol,and propylene glycol; alicyclic compounds having two hydroxyl groups,such as 1,4-bis(hydroxymethyl)cyclohexane; and divalent phenols such asbisphenol A. The polyhydroxy compound also involves compounds havingthree or more hydroxyl groups.

Examples of the polybasic acid include, but are not limited to: divalentcarboxylic acids such as maleic acid, fumaric acid, phthalic acid,isophthalic acid, terephthalic acid, succinic acid, and malonic acid;and trivalent or higher polyvalent carboxylic acids such as1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid,1,2,4-cyclohexanetricarboxylic acid, 1,2,4-naphthalenetricarboxylicacid, 1,2,5-hexanetricarboxylic acid,1,3-dicarboxyl-2-methylenecarboxypropane, and1,2,7,8-octanetetracarboxylic acid. Each of these can be used alone orin combination with others.

Examples of raw material monomers of resins obtained by a condensationpolymerization reaction (e.g., polyester, polyamide,polyester-polyamide) include, in addition to the above-described rawmaterial monomers, monomers for forming amide components such aspolyamines (e.g., ethylenediamine, pentamethylenediamine,hexamethylenediamine, phenylenediamine, triethylenetetramine) andaminocarboxylic acids (e.g., 6-aminocaproic acid, ε-caprolactam). Eachof these can be used alone or in combination with others.

The resin obtained by a condensation polymerization reaction has a glasstransition temperature (Tg) of preferably 55 degrees C. or higher, morepreferably 57 degrees C. or higher, for heat resistance storagestability.

The resin obtained by an addition polymerization reaction is notparticularly limited and can be suitably selected to suit to aparticular application. Examples thereof include vinyl resins obtainedby a radical polymerization.

Examples of raw material monomers of an addition polymerization resininclude, but are not limited to, styrene, o-methylstyrene,m-methylstyrene, p-methylstyrene, α-methyl styrene, p-ethyl styrene, andvinylnaphthalene; unsaturated monoolefins such as ethylene, propylene,butylene, and isobutylene; vinyl esters such as vinyl chloride, vinylbromide, vinyl acetate, and vinyl formate; ethylenic monocarboxylicacids and esters thereof, such as acrylic acid, methyl acrylate, ethylacrylate, n-propyl acrylate, isopropyl acrylate, tert-butyl acrylate,amyl acrylate, methacrylic acid, methyl methacrylate, ethylmethacrylate, n-propyl methacrylate, isopropyl methacrylate, tert-butylmethacrylate, amyl methacrylate, stearyl methacrylate, methoxyethylmethacrylate, glycidyl methacrylate, phenyl methacrylate,dimethylaminoethyl methacrylate, and diethyl aminoethyl methacrylate;ethylenic monocarboxylic acid substitution products such asacrylonitrile, methacrylonitrile, and acrylamide; ethylenic dicarboxylicacids and substitution products thereof such as dimethyl maleate; andvinyl ketones such as vinyl methyl ketone. Each of these can be usedalone or in combination with others.

A cross-linking agent may be added to raw material monomers of theaddition polymerization resin, if necessary.

The cross-linking agent is not particularly limited and can be suitablyselected to suit to a particular application. Examples thereof include,but are not limited to, divinylbenzene, divinylnaphthalene, polyethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, triethyleneglycol diacrylate, dipropylene glycol dimethacrylate, polypropyleneglycol dimethacrylate, and diallyl phthalate. Each of these can be usedalone or in combination with others.

The amount of the cross-linking agent in 100 parts by mass of rawmaterial monomers of the addition polymerization resin is preferablyfrom 0.05 to 15 parts by mass, more preferably from 0.1 to 10 parts bymass. When the amount of the crosslinking agent is 0.05 parts by mass ormore, the effect of addition of the cross-linking agent is exerted. Whenthe amount of the cross-linking agent is 15 parts by mass or less, thetoner is readily melted by heat and well fixed by heat.

It is preferable to use a polymerization initiator when polymerizing rawmaterial monomers of the addition polymerization resin. Thepolymerization initiator is not particularly limited and can be suitablyselected to suit to a particular application. Examples thereof include,but are not limited to: azo-based or diazo-based polymerizationinitiators such as 2,2′-azobis(2,4-dimethylvaleronitrile) and2,2′-azobisisobutyronitrile; and peroxide polymerization initiators suchas benzoyl peroxide, methyl ethyl ketone peroxide, and2,4-dichlorobenzoyl peroxide. Each of these can be used alone or incombination with others.

The amount of the polymerization initiator in 100 parts by mass of rawmaterial monomers of the addition polymerization resin is preferablyfrom 0.05 to 15 parts by mass, more preferably from 0.5 to 10 parts bymass.

Depending on the types of raw materials used, the polymer resulted bythe condensation polymerization reaction or addition polymerizationreaction is either a non-linear polymer having a non-linear structure ora linear polymer having a linear structure.

In the present disclosure, both a non-linear polymer resin (A) and alinear polymer resin (B) are used.

The non-linear polymer resin refers a polymer resin having a substantialcross-linked structure, and the linear polymer resin refers to a polymerresin substantially having no cross-linked structure.

In the present disclosure, it is preferable to use a hybrid resin inwhich a condensation polymerization resin and an addition polymerizationresin are chemically bonded, which is obtained by polymerizing monomersof the both resins using a bireactive compound reactive with the bothresins.

Examples of such a bireactive compound include, but are not limited to,fumaric acid, acrylic acid, methacrylic acid, maleic acid, and dimethylfumarate.

The amount of the bireactive compound in 100 parts by mass of rawmaterial monomers of the addition polymerization resin is preferablyfrom 1 to 25 parts by mass, more preferably from 2 to 10 parts by mass.When the amount of use of the bireactive compound is 1 part by mass ormore, a colorant and a charge controlling agent are well dispersed inthe toner, leading to high image quality. When the amount of use of thebireactive compound is parts by mass or less, the resin isadvantageously not subjected to gelation.

In preparing the hybrid resin, the both reactions need notsimultaneously progress or complete, and may independently progress orcomplete by selecting respective reaction temperatures and times. Forexample, the hybrid resin may be prepared as follows. In a reactionvessel containing a mixture of condensation-polymerizing raw materialmonomers of a polyester resin, another mixture of addition-polymerizingraw material monomers of a vinyl resin and a polymerization initiator isdropped, and these monomers are mixed in advance. After that, first, aradical polymerization reaction of the addition-polymerizing rawmaterial monomers is completed to form the vinyl resin, and next, thereaction temperature is raised to complete a condensation polymerizationreaction of the condensation-polymerizing raw material monomers to formthe polyester resin.

In this method, two reactions independently proceed in the reactionvessel, and two types of resins are thereby effectively dispersed.

The above-described binder resin may be used in combination with anotherresin as long as the performance of the toner is not impaired. Such aresin is not particularly limited and can be suitably selected to suitto a particular application. Examples thereof include, but are notlimited to, polyurethane resin, silicone resin, ketone resin, petroleumresin, and hydrogenated petroleum resin. Each of these can be used aloneor in combination with others.

The amount of the binder resin in the toner is not particularly limitedand can be suitably selected to suit to a particular application.Preferably, the amount of the binder resin in 100 parts by mass of thetoner is from 50 to 95 parts by mass, more preferably from 75 to 90parts by mass.

Colorant

The colorant is not particularly limited and can be suitably selected tosuit to a particular application. Examples thereof include, but are notlimited to, carbon black, Nigrosine dyes, black iron oxide, NAPHTHOLYELLOW S, HANSA YELLOW (10G, 5G and G), Cadmium Yellow, yellow ironoxide, loess, chrome yellow, Titan Yellow, polyazo yellow, Oil Yellow,HANSA YELLOW (GR, A, RN and R), Pigment Yellow L, BENZIDINE YELLOW (Gand GR), PERMANENT YELLOW (NCG), VULCAN FAST YELLOW (5G and R),Tartrazine Lake, Quinoline Yellow Lake, ANTHRAZANE YELLOW BGL,isoindolinone yellow, red iron oxide, red lead, orange lead, cadmiumred, cadmium mercury red, antimony orange, Permanent Red 4R, Para Red,Fire Red, p-chloro-o-nitroaniline red, Lithol Fast Scarlet G, BrilliantFast Scarlet, Brilliant Carmine BS, PERMANENT RED (F2R, F4R, FRL, FRLLand F4RH), Fast Scarlet VD, VULCAN FAST RUBINE B, Brilliant Scarlet G,LITHOL RUBINE GX, Permanent Red FSR, Brilliant Carmine 6B, PigmentScarlet 3B, Bordeaux 5B, Toluidine Maroon, PERMANENT BORDEAUX F2K, HELIOBORDEAUX BL, Bordeaux 10B, BON MAROON LIGHT, BON MAROON MEDIUM, EosinLake, Rhodamine Lake B, Rhodamine Lake Y, Alizarine Lake, Thioindigo RedB, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red, polyazored, Chrome Vermilion, Benzidine Orange, perynone orange, Oil Orange,cobalt blue, cerulean blue, Alkali Blue Lake, Peacock Blue Lake,Victoria Blue Lake, metal-free Phthalocyanine Blue, Phthalocyanine Blue,Fast Sky Blue, INDANTHRENE BLUE (RS and BC), Indigo, ultramarine,Prussian blue, Anthraquinone Blue, Fast Violet B, Methyl Violet Lake,cobalt violet, manganese violet, dioxane violet, Anthraquinone Violet,Chrome Green, zinc green, chromium oxide, viridian, emerald green,Pigment Green B, Naphthol Green B, Green Gold, Acid Green Lake,Malachite Green Lake, Phthalocyanine Green, Anthraquinone Green,titanium oxide, zinc oxide, and lithopone.

The amount of the colorant in the toner is not particularly limited andcan be suitably selected to suit to a particular application.Preferably, the amount of the colorant in 100 parts by mass of the toneris from 1 to 15 parts by mass, more preferably from 3 to 10 parts bymass.

The colorant can be combined with a resin to be used as a master batch.Examples of the resin to be used for manufacturing the master batch orkneaded with the master batch include, but are not limited to: polyesterresins; polymers of styrene or substitutes thereof, such as polystyrene,poly p-chlorostyrene, and polyvinyl toluene; styrene-based copolymerssuch as styrene-p-chlorostyrene copolymer, styrene-propylene copolymer,styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer,styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer,styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer,styrene-methyl methacrylate copolymer, styrene-ethyl methacrylatecopolymer, styrene-butyl methacrylate copolymer, styrene-methylα-chloromethacrylate copolymer, styrene-acrylonitrile copolymer,styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer,styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer,styrene-maleic acid copolymer, and styrene-maleate copolymer; andpolymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride,polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin,epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral,polyacrylic acid resin, rosin, modified rosin, terpene resin, aliphaticor alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinatedparaffin, and paraffin wax. Each of these can be used alone or incombination with others.

The master batch can be obtained by mixing and kneading the resin andthe colorant while applying a high shearing force thereto. To increasethe interaction between the colorant and the resin, an organic solventmay be used. More specifically, the maser batch can be obtained by amethod called flushing in which an aqueous paste of the colorant ismixed and kneaded with the resin and the organic solvent so that thecolorant is transferred to the resin side, followed by removal of theorganic solvent and moisture. This method is advantageous in that theresulting wet cake of the colorant can be used as it is without beingdried. Preferably, the mixing and kneading is performed by a highshearing dispersing device such as a three roll mill.

Other Components

Other components contained in the toner are not particularly limited andcan be suitably selected to suit to a particular application. Examplesthereof include, but are not limited to, a charge controlling agent, afluidity improving agent, a cleanability improving agent, and a magneticmaterial.

Charge Controlling Agent

The charge controlling agent is not particularly limited and can besuitably selected to suit to a particular application. Examples thereofinclude, but are not limited to, nigrosine dyes, triphenylmethane dyes,chromium-containing metal complex dyes, chelate pigments of molybdicacid, Rhodamine dyes, alkoxyamines, quaternary ammonium salts (includingfluorine-modified quaternary ammonium salts), alkylamides, phosphorusand phosphorus-containing compounds, tungsten and tungsten-containingcompounds, fluorine activators, metal salts of salicylic acid, and metalsalts of salicylic acid derivatives.

Specific examples of commercially-available charge controlling agentsinclude, but are not limited to, BONTRON 03 (nigrosine dye), BONTRONP-51 (quaternary ammonium salt), BONTRON S-34 (metal-containing azodye), BONTRON E-82 (metal complex of oxynaphthoic acid), BONTRON E-84(metal complex of salicylic acid), and BONTRON E-89 (phenoliccondensation product), available from Orient Chemical Industries Co.,Ltd.; TP-302 and TP-415 (molybdenum complexes of quaternary ammoniumsalts), available from Hodogaya Chemical Co., Ltd.; LRA-901, and LR-147(boron complex), available from Japan Carlit Co., Ltd.; and cooperphthalocyanine, perylene, quinacridone, azo pigments, and polymershaving a functional group such as a sulfonate group, a carboxyl group,and a quaternary ammonium group.

The amount of the charge controlling agent in the toner is notparticularly limited and can be suitably selected to suit to aparticular application. Preferably, the amount of the charge controllingagent in 100 parts by mass of the toner is from 0.1 to 10 parts by mass,more preferably from 0.2 to 5 parts by mass. When the amount is 10 partsby mass or less, chargeability of the toner is appropriate, the effectof the charge controlling agent is well exerted, the electrostaticattractive force to a developing roller is appropriate, and the fluidityof the developer is good, leading to a high image density. The chargecontrolling agent may be melt-kneaded with the master batch or thebinder resin and thereafter dissolved or dispersed in an organicsolvent, or directly dissolved or dispersed in an organic solvent.Alternatively, the charge controlling agent may be fixed on the surfaceof the resulting toner particles.

Fluidity Improving Agent

The fluidity improving agent is not particularly limited and can besuitably selected to suit to a particular application as long as itreforms a surface to improve hydrophobicity for preventing deteriorationof fluidity and chargeability even under high-humidity environments.Specific examples thereof include, but are not limited to, silanecoupling agents, silylation agents, silane coupling agents having afluorinated alkyl group, organic titanate coupling agents, aluminumcoupling agents, silicone oils, and modified silicone oils. Preferably,the above-described silica and titanium oxide are surface-treated withsuch a fluidity improving agent to become hydrophobic silica andhydrophobic titanium oxide, respectively.

Cleanability Improving Agent

The cleanability improving agent is not particularly limited and can besuitably selected to suit to a particular application as long as it isadded to the toner for facilitating removal of the developer remainingon a photoconductor or primary transfer medium after image transfer.Specific examples thereof include, but are not limited to, metal saltsof fatty acids (e.g., zinc stearate, calcium stearate) and polymerparticles prepared by soap-free emulsion polymerization (e.g.,polymethyl methacrylate particles, polystyrene particles). Preferably,the polymer particles have a relatively narrow particle sizedistribution and a volume average particle diameter of from 0.01 to 1μm.

Magnetic Material

The magnetic material is not particularly limited and can be suitablyselected to suit to a particular application. Examples thereof include,but are not limited to, iron powder, magnetite, and ferrite. Inparticular, those having white color tone are preferred.

A method for producing the toner according to an embodiment of thepresent invention is not particularly limited and can be suitablyselected to suit to a particular application. For example, the methodmay include the processes of mixing a binder resin, a colorant, and arelease agent optionally along with other components using a mixer,kneading the mixture using a kneader such as a heat roll and anextruder, cooling the kneaded product for solidification, pulverizingthe cooled product using a pulverizer such as a jet mill, andclassifying the pulverized product, to obtain toner base particles. Thetoner base particles thus prepared are then mixed with external additiveparticles, thus preparing a toner.

The method for producing the toner is not particularly limited, and anyof bulk polymerization, solution polymerization, emulsionpolymerization, and suspension polymerization can be employed.

Toner Accommodating Unit

In the present disclosure, a toner accommodating unit refers to a unithaving a function of accommodating toner, that is accommodating thetoner. The toner accommodating unit may be in the form of, for example,a toner accommodating container, a developing device, or a processcartridge.

The toner accommodating container refers to a container accommodatingthe toner.

The developing device refers to a device accommodating the toner andhaving a developing unit configured to develop an electrostatic latentimage into a toner image with the toner.

The process cartridge refers to a combined body of an electrostaticlatent image bearer (also referred to as an image bearer) with adeveloping unit accommodating the toner, detachably mountable on animage forming apparatus. The process cartridge may further include atleast one selected from a charger, an irradiator, and a cleaner.

The toner accommodating unit according to an embodiment of the presentinvention is capable of forming images, when mounted on an image formingapparatus, utilizing the properties of the above-described toner thatforms high-density images while preventing generation of fog images in alow-temperature low-humidity environment (at a temperature of degrees C.and a relative humidity of 15%).

Developer

A developer according to an embodiment of the present invention containsthe toner according to an embodiment of the present invention and acarrier.

The carrier is not particularly limited and can be suitably selected tosuit to a particular application. Preferably, the carrier comprises acore material and a resin layer coating the core material.

The core material is not particularly limited and can be suitablyselected from known ones. Examples thereof include, but are not limitedto, manganese-strontium (Mn—Sr) materials and manganese-magnesium(Mn—Mg) materials having a magnetization of from 50 to 90 emu/g. Forsecuring image density, high magnetization materials such as ironpowders having a magnetization of 100 emu/g or more and magnetiteshaving a magnetization of from 75 to 120 emu/g are preferred.Additionally, low magnetization materials such as copper-zinc (Cu—Zn)materials having a magnetization of from 30 to 80 emu/g are preferredfor improving image quality, because such materials are capable ofreducing the impact of the magnetic brush to a photoconductor. Each ofthese can be used alone or in combination with others.

The core material has a volume average particle diameter (D50) ofpreferably from 10 to 200 μm, more preferably from 40 to 100 μm.

The material of the resin layer is not particularly limited and can besuitably selected from known resins to suit to a particular application.Examples thereof include, but are not limited to, amino resin, polyvinylresin, polystyrene resin, halogenated olefin resin, polyester resin,polycarbonate resin, polyethylene resin, polyvinyl fluoride resin,polyvinylidene fluoride resin, polytrifluoroethylene resin,polyhexafluoropropylene resin, copolymer of vinylidene fluoride with anacrylic monomer, copolymer of vinylidene fluoride with vinyl fluoride,fluoroterpolymer (e.g., terpolymer of tetrafluoroethylene, vinylidenefluoride, and non-fluoride monomer), and silicone resin. Each of thesecan be used alone or in combination with others.

Specific examples of the amino resin include, but are not limited to,urea-formaldehyde resin, melamine resin, benzoguanamine resin, urearesin, polyamide resin, and epoxy resin. Specific examples of thepolyvinyl resin include, but are not limited to, acrylic resin,polymethyl methacrylate resin, polyacrylonitrile resin, polyvinylacetate resin, polyvinyl alcohol resin, and polyvinyl butyral resin.Specific examples of the polystyrene resin include, but are not limitedto, polystyrene resin and styrene-acrylic copolymer resin. Specificexamples of the halogenated olefin resin include, but are not limitedto, polyvinyl chloride. Specific examples of the polyester resininclude, but are not limited to, polyethylene terephthalate resin andpolybutylene terephthalate resin.

The resin layer may contain a conductive powder, as necessary. Specificexamples of the conductive powder include, but are not limited to, metalpowder, carbon black, titanium oxide, tin oxide, and zinc oxide.Preferably, the conductive powder has an average particle diameter of 1μm or less. When the average particle diameter is 1 μm or less, it isadvantageously easy to control electrical resistance.

The resin layer can be formed by, for example, dissolving the siliconeresin, etc., in a solvent to prepare a coating liquid and uniformlycoating the surface of the core material with the coating liquid by aknown coating method, followed by drying and baking. Examples of thecoating method include, but are not limited to, a dipping method, aspraying method, and a brush coating method.

The solvent is not particularly limited and can be suitably selected tosuit to a particular application. Examples thereof include, but are notlimited to, toluene, xylene, methyl ethyl ketone, methyl isobutylketone, cellosolve, and butyl acetate.

The baking method is not particularly limited and may be either anexternal heating method or an internal heating method, such as a methodusing a stationary electric furnace, fluid electric furnace, rotaryelectric furnace, or burner furnace, and a method using microwave.

Preferably, the proportion of the resin layer in the carrier is from0.01% to 5.0% by mass.

When the proportion is 0.01% by mass or more, the resin layer can beuniformly formed on the surface of the core material. When theproportion is 5.0% by mass or less, the thickness of the resin layerbecomes appropriate and uniform carrier particles are produced.

The proportion of the carrier in the two-component developer is notparticularly limited and can be suitably selected to suit to aparticular application, but is preferably from 90% to 98% by mass, morepreferably from 93% to 97% by mass.

In the two-component developer, preferably, 1 to 10.0 parts by mass ofthe toner is mixed with 100 parts by mass of the carrier.

The developer according to an embodiment of the present inventioncontains the toner according to an embodiment of the present inventionand is therefore capable of producing high-density images whilepreventing generation of fog images over time in low-temperaturelow-humidity environments.

The developer according to an embodiment of the present invention can besuitably used for electrophotographic image formation, particularlypreferably used for a developing device, a process cartridge, an imageforming apparatus, and an image forming method described below accordingto some embodiments of the present invention.

Process Cartridge

The process cartridge according to an embodiment of the presentinvention includes: an electrostatic latent image bearer configured tobear an electrostatic latent image; and a developing device configuredto develop the electrostatic latent image on the electrostatic latentimage bearer with the developer to form a visible image. The processcartridge may further include other devices appropriately selectedaccording to need.

The developing device includes at least a developer accommodatingcontainer containing the toner or developer according to an embodimentof the present invention, and a developer bearer configured to bear andconvey the toner or developer contained in the developer accommodatingcontainer. The developing device may further include a layer thicknessregulator configured to regulate the layer thickness of the toner borneby the developer bearer.

The process cartridge is detachably mountable on various image formingapparatuses. Preferably, the process cartridge is detachably mounted onthe image forming apparatus according to an embodiment of the presentinvention to be described later.

The toner according to an embodiment of the present invention, whenloaded in an image forming apparatus having the process cartridge,exhibits excellent effects in forming images. The toner according to anembodiment of the present invention thus provides a process cartridgethat forms images with excellent quality.

FIG. 2 is a schematic view of a process cartridge according to anembodiment of the present invention. A process cartridge 1 illustratedin FIG. 2 includes a photoconductor 2, a charger 3, a developing device4, and a cleaner 5.

In an image forming apparatus having the process cartridge, thephotoconductor 2 is rotationally driven at a predetermined peripheralvelocity.

During rotation of the photoconductor 2, a circumferential surface ofthe photoconductor 2 is uniformly charged to a predetermined positive ornegative potential by the charger 3, and then irradiated with lightemitted from an irradiator by slit exposure or laser beam scanningexposure, so that electrostatic latent images are sequentially formed onthe circumferential surface of the photoconductor 2. The electrostaticlatent images thus formed are subsequently developed into toner imagesby the developing device 4. The toner images are sequentiallytransferred onto a recording medium fed from a sheet feeder to betweenthe photoconductor 2 and a transfer device in synchronization withrotation of the photoconductor 2.

An image forming apparatus according to an embodiment of the presentinvention includes: an electrostatic latent image bearer; a chargerconfigured to charge a surface of the electrostatic latent image bearer;an irradiator configured to irradiate the charged surface of theelectrostatic latent image bearer to from an electrostatic latent imagethereon; a developing device configured to develop the electrostaticlatent image with a developer to form a visible image; a transfer deviceconfigured to transfer the visible image onto a recording medium; and afixing device configured to fix the visible image on the recordingmedium. Here, the developing device is the above-described developingdevice according to an embodiment of the present invention.

An image forming method according to an embodiment of the presentinvention includes the processes of: charging a surface of anelectrostatic latent image bearer; irradiating the charged surface ofthe electrostatic latent image bearer to form an electrostatic latentimage thereon; developing the electrostatic latent image with thedeveloper according to an embodiment of the present invention to form avisible image; transferring the visible image onto a recording medium;and fixing the visible image on the recording medium.

FIG. 3 is a schematic view of an image forming apparatus according to anembodiment of the present invention. This image forming apparatusincludes a charger 132, an irradiator 133, a developing device 140, atransfer device 150, a cleaner 160, and a neutralization lamp 170, eachof which being disposed around a photoconductor 120 having a drum-likeshape. The charger 132 and the photoconductor 120 are out of contactwith each other forming a gap having a distance of about 0.2 mmtherebetween. The charger 132 charges the photoconductor 120 by formingan electric field in which an alternating current component issuperimposed on a direct current component by a voltage applicator, thuseffectively reducing charging unevenness.

FIG. 4 is an enlarged schematic view of a main part of FIG. 3. Adeveloping sleeve 141 is disposed within a space formed between thephotoconductor 120 and a toner hopper 145. The developing sleeve 141 isdriven to rotate in a direction indicated by arrow in FIG. 4. Inside thedeveloping sleeve 141, magnets serving as magnetic field generators aredisposed with the relative positions thereof invariant to the developingdevice, for forming a magnetic brush of carriers 123.

A doctor blade 143 is integrally installed to one side of a developerhousing 142 opposite to a side to which a support casing 144 isinstalled. An edge of the doctor blade 143 is disposed facing the outercircumferential surface of the developing sleeve 141 forming a constantgap therebetween.

With the above configuration, a toner 121 is fed from the toner hopper145 to a developer container 146 by a toner agitator 148 and a tonersupply mechanism 149. The toner 121 is then stirred by a developerstirring mechanism 147 to be given a desired triboelectric/separationcharge. The charged toner 121 is carried on the developing sleeve 141together with the carriers 123 and conveyed to a position where thedeveloping sleeve 141 faces the outer circumferential surface of thephotoconductor 120. The toner 121 is electrostatically bound to anelectrostatic latent image formed on the photoconductor 120, thusforming a toner image on the photoconductor 120.

The recording medium having the transferred image thereon is separatedfrom the surface of the photoconductor and introduced to a fixing deviceso that the image is fixed thereon. The recording medium having thefixed image thereon is printed out the apparatus as a copy.

After the image has been transferred, the surface of the photoconductoris cleaned by removing residual toner particles by the cleaner 5 andfurther electrically neutralized to be repeatedly used for imageformation.

The toner according to an embodiment of the present invention, whenloaded in an image forming apparatus having a contact charger, exhibitsexcellent effects in forming images. Thus, the toner according to anembodiment of the present invention provides an image forming apparatusequipped with a charger with less ozone emission.

FIG. 5 is a schematic view of an image forming apparatus having acharger that performs roller charging.

A drum-shaped photoconductor 10, serving as a to-be-charged member andan image bearer, is rotationally driven at a predetermined speed(process speed) in the direction indicated by arrow in FIG. 5.

A charging roller 11, serving as a charging member, is in contact withthe photoconductor 10. The charging roller 11 includes a core metal 12and a conductive rubber layer 13 that is concentrically and integrallyformed on the outer circumferential surface of the core metal 12. Withboth ends of the core metal 12 being rotatably held by bearings, thecharging roller 11 is pressed against the photoconductor 10 with apredetermined pressing force by a pressurization assembly. In FIG. 5,the charging roller 11 rotates following rotary drive of thephotoconductor 10.

The charging roller 11 is formed of a core metal having a diameter of 9mm and a medium resistance rubber layer having a resistivity of about100,000 Ω·cm formed thereon, so that the charging roller 11 has adiameter of 16 mm.

As illustrated in FIG. 5, the core metal 12 of the charging roller 11 iselectrically connected to a power source 14, and the power source 14applies a predetermined bias to the charging roller 11. As a result, thecircumferential surface of the photoconductor 10 is uniformly charged tohave predetermined polarity and potential.

FIG. 6 is a schematic view of an image forming apparatus having acharger that performs brush charging.

A drum-shaped photoconductor 20, serving as a to-be-charged member andan image bearer, is rotationally driven at a predetermined speed(process speed) in the direction indicated by arrow in FIG. 6.

A fur brush roller 21 is in contact with the photoconductor 20 at apredetermined nip width with a predetermined pressing force against theelasticity of a brush 23.

The fur brush roller 21, serving as a contact charging member, includesa core metal 22 and the brush 23. The core metal 22 has a diameter of 6mm and is also serving as an electrode. The brush 23 is composed of apile fabric tape made of a conductive rayon fiber REC-B manufactured byUNITIKA LTD. and is spirally wound around the core metal 22. The furbrush roller 21 is thus formed into a roll brush having an outerdiameter of 14 mm and a longitudinal length of 250 mm.

The filaments of the brush 23 are 300 denier/50 filaments, and thedensity is 155 filaments per square millimeter.

This roll brush has been inserted into a pipe having an inner diameterof 12 mm by being rotated in one direction, with the roll brush and thepipe being concentric with each other, and left in a high-temperaturehigh-humidity atmosphere to make the filaments slanted.

The resistance value of the fur brush roller 21 is 1×10⁵Ω when a voltageof 100 V is applied.

This resistance value has been converted from the current flowing whenthe fur brush roller 21 is brought into contact with a metallic drumhaving a diameter of 30 mm at a nip width of 3 mm and a voltage of 100 Vis applied thereto.

The resistance value of the fur brush charger is preferably 10⁴Ω or moreso as to prevent, when a low pressure-resistant defective portion suchas a pinhole occurs on the photoconductor 20 as a charged member, anexcessive leak current from flowing into this portion to preventdefective charging of the charging nip portion and further defectiveimages. The resistance value is more preferably 10⁷Ω or less so thatcharges can be sufficiently injected into the surface of thephotoconductor 20.

The brush may be made of, for example, REC-B as described above, REC-C,REC-M1, or REC-M10 manufactured by UNITIKA LTD., SA-7 manufactured byToray Industries, Inc., THUNDERON manufactured by Nihon Sanmo DyeingCo., Ltd., BELLTRON manufactured by Kanebo, Ltd. (now available from KBSEIREN, LTD.), CLACARBO manufactured by Kuraray Co., Ltd., rayon withcarbon dispersed, or ROVAL manufactured by Mitsubishi Rayon Co., Ltd.

Preferably, each filament of the brush is from 3 to 10 denier, and thedensity of filaments is from 10 to 100 filaments/bundle and from 80 to600 filaments/mm. The length of each filament is preferably from 1 to 10mm.

The fur brush roller 21 is rotationally driven in a direction oppositeto the direction of rotation of the photoconductor 20, so that the furbrush roller 21 is brought into contact with the surface of thephotoconductor with a speed difference. The fur brush roller 21 is thenapplied with a predetermined charging voltage from a power source 24, sothat the surface of the photoconductor is uniformly contact-charged tohave predetermined polarity and potential.

In contact-charging the photoconductor 20 by the fur brush roller 21,direct injection charging is dominant. The surface of the photoconductor20 is charged to a potential approximately equal to the charging voltageapplied to the fur brush roller 21.

In the case of magnetic brush charging, as in the case of fur brushcharging, the magnetic brush is in contact with the photoconductor 20 ata predetermined nip width with a predetermined pressing force againstthe elasticity of the brush 23.

The magnetic brush as a contact charging member may be composed ofmagnetic particles that are ferrite particles coated with a mediumresistance resin layer. As an example, the ferrite particles is amixture of Zn—Cu ferrite particles having an average particle diameterof 25 μm and Zn—Cu ferrite particles having an average particle diameterof 10 μm mixed at a mass ratio of 1:0.05, whose particle diameterdistribution has two peaks at each of the average particle diameters.

The contact charging member may be composed of the above-describedcoated magnetic particles, a non-magnetic conductive sleeve forsupporting the magnetic particles, and a magnet roll contained in thenon-magnetic conductive sleeve. The coated magnetic particles are madeto coat the conductive sleeve with a thickness of 1 mm, and a chargingnip having a width of about 5 mm is formed of the conductive sleeve toface the photoconductor 20.

A gap between the conductive sleeve holding the coated magneticparticles and the photoconductor may be set to about 500 μm.

The magnet roll is rotated so that the surface of the sleeve rubs thesurface of the photoconductor in the opposite direction at a speed twiceas fast as the circumferential speed of the surface of thephotoconductor. The photoconductor and the magnetic brush thus come intouniform contact with each other.

EXAMPLES

Further understanding can be obtained by reference to certain specificexamples which are provided herein for the purpose of illustration onlyand are not intended to be limiting. In the following descriptions,“parts” represent “parts by mass” unless otherwise specified.

In the following Examples, the softening temperature, the glasstransition temperature, and the weight average molecular weight ofresins were measured as follows.

Measurement of Softening Temperature (Tm) and Glass TransitionTemperature (Tg) of Resins

The softening temperature (Tm) was measured according to the methoddescribed in JIS (Japanese Industrial Standards) K72101 using acapillary rheometer flowtester (manufactured by Shimadzu Corporation).First, 1 cm³ of a sample was applied with a load of 20 kg/cm² by aplunger, while being heated at a temperature rising rate of 6 degreesC./min, to be extruded from a nozzle having a diameter of 1 mm and alength of 1 mm. As a result, a plunger drop amount-temperature curve,which was an S-shaped curve, was drawn. The height of the S-shaped curvewas defined as h, and the temperature corresponding to h/2 (i.e., thetemperature at which half the resin flowed out) was taken as thesoftening temperature (Tm).

The glass transition temperature (Tg) was measured using a differentialscanning calorimeter (DSC-60 manufactured by Shimadzu Corporation) bysubjecting the sample to heating from room temperature (25 degrees C.)to 200 degrees C. at a rate of 10 degrees C./min, then cooling to roomtemperature at a rate of 10 degrees C./min, and heating again a rate of10 degrees C./min. In the resulted curve, the height between thebaseline below the glass transition point and the other baseline abovethe glass transition point was defined as h, and the temperaturecorresponding to ½ of h was taken as the glass transition temperature(Tg).

Weight Average Molecular Weight (Mw) of Resins

The weight average molecular weight was measured using a GPC (gelpermeation chromatography) instrument HLC-8220GPC (available from TosohCorporation) equipped with triple columns TSKgel SuperHZM-H 15 cm(available from Tosoh Corporation). Specifically, the columns werestabilized in a heat chamber at 40 degrees C. Next, tetrahydrofuran(THF) was allowed to flow in the columns at a flow rate of 1 mL/min, and50 to 200 μL of a 0.05-0.6% by mass THF solution of a sample wasinjected into the instrument to measure the weight average molecularweight of the sample. The molecular weight of the sample was determinedfrom a calibration curve, created with several types of monodispersepolystyrene standard samples, that shows the relation between thelogarithmic values of molecular weights and the number of counts.

The polystyrene standard samples were those having respective weightaverage molecular weights of 6×10², 2.1×10³, 4×10³, 1.75×10⁴, 5.1×10⁴,1.1×10⁵, 3.9×10⁵, 8.6×10⁵, 2×10⁶, and 4.48×10⁶ (available from PressureChemical Co. or Tosoh Corporation).

As the detector, a refractive index (RI) detector was used.

Production Example 1 of Non-Linear Polyester Resin Production ofNon-Linear Polyester Resin A

In a flask equipped with a stainless steel stirrer, a flow-downcondenser, a nitrogen gas inlet tube, and a thermometer, 9.0 mol offumaric acid, 3.5 mol of trimellitic anhydride, 5.5 mol of bisphenol A(2,2) propylene oxide, 3.5 mol of bisphenol A (2,2) ethylene oxide werestirred and subjected to a condensation polymerization reaction under anitrogen atmosphere at 230 degrees C. Thus, a non-linear polyester resinA was prepared.

The non-linear polyester resin A was found to have a softeningtemperature (Tm) of 145.1 degrees C., a glass transition temperature(Tg) of 61.5 degrees C., and a weight average molecular weight (Mw) of82,000.

Production Example 2 of Linear Polyester Resin Production of LinearPolyester Resin B

In a flask equipped with a stainless steel stirrer, a flow-downcondenser, a nitrogen gas inlet tube, and a thermometer, 7 mol ofterephthalic acid, 2.5 mol of trimellitic anhydride, 5.5 mol ofbisphenol A (2,2) propylene oxide, 3.5 mol of bisphenol A (2,2) ethyleneoxide were stirred and subjected to a condensation polymerizationreaction under a nitrogen atmosphere at 230 degrees C. Thus, a linearpolyester resin B was prepared.

The linear polyester resin B was found to have a softening temperature(Tm) of 102.8 degrees C., a glass transition temperature (Tg) of 61.2degrees C., and a weight average molecular weight (Mw) of 8,000.

Production Example 1 of Hybrid Resin Production of Hybrid Resin C

In a dropping funnel, 18 mol of styrene and 4.5 mol of butylmethacrylate as addition-polymerization reactive monomers, and 0.35 molof t-butyl hydroperoxide as a polymerization initiator were put. In aflask equipped with a stainless steel stirrer, a flow-down condenser, anitrogen gas inlet tube, and a thermometer, 9.0 mol of fumaric acid asan addition-polymerization-condensation-polymerization bireactivemonomer, 3.5 mol of trimellitic anhydride, 5.5 mol of bisphenol A (2,2)propylene oxide, and 3.8 mol of bisphenol A (2,2) ethylene oxide ascondensation-polymerization reactive monomers, and 58 mol of dibutyltinoxide as an esterification catalyst were stirred under a nitrogenatmosphere at 138 degrees C., and the mixture of addition-polymerizationraw materials was dropped therein from the dropping funnel over a periodof 4 hours.

After that, an aging was performed for 6 hours while maintaining thetemperature at 138 degrees C., then the temperature was raised to 230degrees C. to conduct a reaction. Thus, a hybrid resin C was prepared.

The hybrid resin C was found to have a softening temperature (Tm) of151.5 degrees C. and a glass transition temperature (Tg) of 62.1 degreesC.

The hybrid resin C was found to be a composition of a polyester resin(having a weight average molecular weight (Mw) of 48,000) and astyrene-acrylic copolymer resin (having a weight average molecularweight (Mw) of 190,000), and the mass ratio therebetween was 78/22.

Preparation of Toner Base Particles A

Toner Materials

-   -   Non-linear polyester resin A: 42 parts by mass    -   Linear polyester resin B: 45 parts by mass    -   Hybrid resin C: 13 parts by mass    -   Carbon black: 18 parts by mass    -   Charge controlling agent (SPILON BLACK TR-H manufactured by        Hodogaya Chemical Co., Ltd.): 2.5 parts by mass    -   Release Agent (Low-molecular-weight polypropylene, having a        weight average molecular weight (Mw) of 5,500): 2.6 parts by        mass

The above toner materials were stirred and mixed using a HENSCHEL MIXER.The mixture was heat-melted using a roll mill at a temperature of from125 to 130 degrees C. for 40 minutes, then cooled to room temperature(25 degrees C.). The resulted kneaded product was pulverized andclassified using a jet mill. Thus, toner base particles A were preparedhaving a volume average particle diameter of 7.0 μm and a particlediameter distribution in which the proportion of particles having aparticle diameter of 5 μm or less was 35% by number.

Preparation of Toner Base Particles B

Toner Material s

-   -   Release Agent (Low-molecular-weight polypropylene, having a        weight average molecular weight (Mw) of 5,500): 5.0 parts by        mass Toner base particles B were prepared in the same manner as        the toner base particles A except for the above change in toner        materials.

Preparation of Toner Base Particles C

Toner Materials

-   -   Release Agent (Low-molecular-weight polypropylene, having a        weight average molecular weight (Mw) of 5,500): 2.4 parts by        mass Toner base particles C were prepared in the same manner as        the toner base particles A except for the above change in toner        materials.

Preparation of Toner Base Particles D

Toner Materials

-   -   Release Agent (Low-molecular-weight polypropylene, having a        weight average molecular weight (Mw) of 5,500): 5.2 parts by        mass Toner base particles D were prepared in the same manner as        the toner base particles A except for the above change in toner        materials.

In the present disclosure, pseudoboehmite particles were prepared by thefollowing procedure.

An aluminum alkoxide is once hydrolyzed to obtain an alumina hydrate.The alumina hydrate thus obtained was purified by a distillationoperation to obtain a high-purity aluminum alkoxide. By changing thehydrolysis conditions and drying conditions of the aluminum alkoxide,alumina hydrates, i.e., pseudoboehmite particles, of various phaseshaving different particle sizes were obtained.

Preparation of Pseudoboehmite Particle Base A

Pseudoboehmite particles were prepared based on the above-describedprocedure. It was confirmed by X-ray diffraction that a pseudoboehmitephase had been created. The particles thus prepared was found to have ad50 of 8 nm and a ratio (Dv/Dn) of volume average particle diameter Dvto number average particle diameter Dn of 1.3, as measured by a laserdiffraction particle size distribution analyzer LA-750 (manufactured byHORIBA, Ltd.). Thus, a pseudoboehmite particle base A was prepared.

Preparation of Pseudoboehmite Particle Base B

Pseudoboehmite particles were prepared based on the above-describedprocedure. It was confirmed by X-ray diffraction that a pseudoboehmitephase had been created. The particles thus prepared was found to have ad50 of 120 nm and a ratio Dv/Dn of 1.2, as measured by a laserdiffraction particle size distribution analyzer LA-750 (manufactured byHORIBA, Ltd.). Thus, a pseudoboehmite particle base B was prepared.

Preparation of Pseudoboehmite Particle Base C

Pseudoboehmite particles were prepared based on the above-describedprocedure. It was confirmed by X-ray diffraction that a pseudoboehmitephase had been created. The particles thus prepared was found to have ad50 of 5 nm and a ratio Dv/Dn of 1.2, as measured by a laser diffractionparticle size distribution analyzer LA-750 (manufactured by HORIBA,Ltd.). Thus, a pseudoboehmite particle base C was prepared.

Preparation of Pseudoboehmite Particle Base D

Pseudoboehmite particles were prepared based on the above-describedprocedure. It was confirmed by X-ray diffraction that a pseudoboehmitephase had been created. The particles thus prepared was found to have ad50 of 135 nm and a ratio Dv/Dn of 1.2, as measured by a laserdiffraction particle size distribution analyzer LA-750 (manufactured byHORIBA, Ltd.). Thus, a pseudoboehmite particle base D was prepared.

Preparation of Amorphous Aluminum Hydroxide Particles

Amorphous aluminum hydroxide particles were prepared. It was confirmedby X-ray diffraction that an amorphous aluminum hydroxide phase had beencreated. The particles thus prepared was found to have a d50 of 108 nmand a ratio Dv/Dn of 1.2, as measured by a laser diffraction particlesize distribution analyzer LA-750 (manufactured by HORIBA, Ltd.).

Preparation of Bayerite Particles

Bayerite particles were prepared. It was confirmed by X-ray diffractionthat a bayerite phase had been created. The particles thus prepared wasfound to have a d50 of 25 nm and a ratio Dv/Dn of 1.2, as measured by alaser diffraction particle size distribution analyzer LA-750(manufactured by HORIBA, Ltd.).

Production Example 1 of External Additive AA

The pseudoboehmite particle base A was put in a reaction vessel, and amixed solution of 4 g of heptadecafluorodecyltrimethoxysilane and 0.5 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive AA was prepared.

Production Example 2 of External Additive AB

The pseudoboehmite particle base A was put in a reaction vessel, and amixed solution of 8 g of heptadecafluorodecyltrimethoxysilane and 1.8 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive AB was prepared.

Production Example 3 of External Additive AD

The pseudoboehmite particle base A was put in a reaction vessel, and amixed solution of 3.8 g of heptadecafluorodecyltrimethoxysilane and 0.4g of hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive AD was prepared.

Production Example 4 of External Additive BA

The pseudoboehmite particle base B was put in a reaction vessel, and amixed solution of 4 g of heptadecafluorodecyltrimethoxysilane and 0.5 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive BA was prepared.

Production Example 5 of External Additive BB

The pseudoboehmite particle base B was put in a reaction vessel, and amixed solution of 8 g of heptadecafluorodecyltrimethoxysilane and 1.8 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive BB was prepared.

Production Example 6 of External Additive BE

The pseudoboehmite particle base B was put in a reaction vessel, and amixed solution of 8.2 g of heptadecafluorodecyltrimethoxysilane and 2.0g of hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive BE was prepared.

Production Example 7 of External Additive CB

The pseudoboehmite particle base C was put in a reaction vessel, and amixed solution of 8 g of heptadecafluorodecyltrimethoxysilane and 1.8 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive CB was prepared.

Production Example 8 of External Additive DA

The pseudoboehmite particle base D was put in a reaction vessel, and amixed solution of 4 g of heptadecafluorodecyltrimethoxysilane and 0.5 gof hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive DA was prepared.

Production Example 9 of External Additive EC

The above-prepared amorphous aluminum hydroxide particles were put in areaction vessel, and a mixed solution of 5 g ofheptadecafluorodecyltrimethoxysilane and 0.9 g of hexamethyldisilazanewas sprayed on 100 g of the pseudoboehmite particle base powder understirring in a nitrogen atmosphere. The pseudoboehmite particle base wasthen heat-stirred at 220 degrees C. for 150 minutes and then cooled.Thus, an external additive EC was prepared.

Production Example 10 of External Additive FC

The above-prepared bayerite particles were put in a reaction vessel, anda mixed solution of 5 g of heptadecafluorodecyltrimethoxysilane and 0.9g of hexamethyldisilazane was sprayed on 100 g of the pseudoboehmiteparticle base powder under stirring in a nitrogen atmosphere. Thepseudoboehmite particle base was then heat-stirred at 220 degrees C. for150 minutes and then cooled. Thus, an external additive EC was prepared.

Production Example 11 of External Additive GA

An alumina powder having a BET specific surface area of 200 m²/g was putin a reaction vessel, and a mixed solution of 4 g ofheptadecafluorodecyltrimethoxysilane and 0.5 g of hexamethyldisilazanewas sprayed on 100 g of the alumina powder under stirring in a nitrogenatmosphere. The alumina powder was then heat-stirred at 220 degrees C.for 150 minutes and then cooled. Thus, an external additive GA wasprepared.

Production Example 12 of External Additive HA

An alumina powder having a BET specific surface area of 20 m²/g was putin a reaction vessel, and a mixed solution of 4 g ofheptadecafluorodecyltrimethoxysilane and 0.5 g of hexamethyldisilazanewas sprayed on 100 g of the alumina powder under stirring in a nitrogenatmosphere. The alumina powder was then heat-stirred at 220 degrees C.for 150 minutes and then cooled. Thus, an external additive HA wasprepared.

Example 1

Next, 100 parts by mass of the toner base particles A were stir-mixedwith 1.2 parts by mass of a silica (R-972 manufactured by Clariant JapanK.K.) and 0.5 parts by mass of the external additive AA using a HENSCHELMIXER under the following mixing conditions, then allowed to passthrough a mesh to remove coarse particles. Thus, a toner A was prepared.

Mixing Conditions

-   -   Frequency: 80 Hz    -   Time: 10 min

Example 2

A toner B was prepared in the same manner as in Example 1 except forreplacing the toner base particles A with the toner base particles B.

Example 3

A toner C was prepared in the same manner as in Example 1 except forreplacing the external additive AA with the external additive AB.

Example 4

A toner D was prepared in the same manner as in Example 1 except forreplacing the toner base particles A with the toner base particles B andreplacing the external additive AA with the external additive AB.

Example 5

A toner E was prepared in the same manner as in Example 1 except forchanging the amount of the external additive AA to 2.0 parts.

Example 6

A toner F was prepared in the same manner as in Example 5 except forreplacing the toner base particles A with the toner base particles B.

Example 7

A toner G was prepared in the same manner as in Example 5 except forreplacing the external additive AA with the external additive AB.

Example 8

A toner H was prepared in the same manner as in Example 5 except forreplacing the toner base particles A with the toner base particles B andreplacing the external additive AA with the external additive AB.

Example 9

A toner I was prepared in the same manner as in Example 1 except forreplacing the external additive AA with the external additive BA.

Example 10

A toner J was prepared in the same manner as in Example 9 except forreplacing the toner base particles A with the toner base particles B.

Example 11

A toner K was prepared in the same manner as in Example 9 except forreplacing the external additive AA with the external additive BB.

Example 12

A toner L was prepared in the same manner as in Example 9 except forreplacing the toner base particles A with the toner base particles B andreplacing the external additive AA with the external additive BB.

Example 13

A toner M was prepared in the same manner as in Example 9 except forchanging the amount of the external additive BA to 2.0 parts.

Example 14

A toner N was prepared in the same manner as in Example 13 except forreplacing the toner base particles A with the toner base particles B.

Example 15

A toner O was prepared in the same manner as in Example 13 except forreplacing the external additive AA with the external additive BB.

Example 16

A toner P was prepared in the same manner as in Example 13 except forreplacing the toner base particles A with the toner base particles B andreplacing the external additive AA with the external additive BB.

Example 17

A toner Q was prepared in the same manner as in Example 1 except forreplacing the toner base particles A with the toner base particles B andreplacing the external additive AA with the external additive EC in anamount of 1.0 part.

Example 18

A toner R was prepared in the same manner as in Example 17 except forreplacing the external additive EC with the external additive FC.

Comparative Example 1

A toner AA was prepared in the same manner as in Example 1 except forreplacing the external additive AA with the external additive GA in anamount of 2.0 parts.

Comparative Example 2

A toner AB was prepared in the same manner as in Comparative Example 1except for changing the amount of the external additive GA to 0.5 parts.

Comparative Example 3

A toner AC was prepared in the same manner as in Comparative Example 2except for replacing the external additive GA with the external additiveHA.

Example 19

A toner AD was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles B and replacing the external additive GA with the externaladditive CB.

Example 20

A toner AE was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles B and replacing the external additive GA with the externaladditive DA in an amount of 0.5 parts.

Example 21

A toner AF was prepared in the same manner as in Comparative Example 1except for replacing the external additive GA with the external additiveBA in an amount of 0.4 parts.

Example 22

A toner AG was prepared in the same manner as in Comparative Example 1except for replacing the external additive GA with the external additiveAB in an amount of 2.1 parts.

Example 23

A toner AH was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles B and replacing the external additive GA with the externaladditive AD.

Example 24

A toner AI was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles B and replacing the external additive GA with the externaladditive BE in an amount of 0.5 parts.

Example 25

A toner AJ was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles C and replacing the external additive GA with the externaladditive AA in an amount of 0.5 parts.

Example 26

A toner AK was prepared in the same manner as in Comparative Example 1except for replacing the toner base particles A with the toner baseparticles D and replacing the external additive GA with the externaladditive BA.

Measurement of Aluminum Density X1 and Fluorine Density X2 by XPS

-   -   Analysis equipment: AXIS-ULTRA (manufactured by Shimadzu        Corporation)    -   X-ray: 15 kV, 9 mA, Hybrid    -   Neutralization gun: 2.0 A (F-Current), 1.3 V (F-Bias), 1.8 V        (C-Balance)    -   Step: 0.1 eV (Narrow), 2.0 eV (Wide)    -   Pass E: 20 eV (Narrow), 160 eV (Wide)    -   Relative sensitivity coefficient: Use the relative sensitivity        coefficient of Casa XPS    -   Sample preparation: A toner sample was put in an aluminum-made        chip having a cylindrical recess having a depth of 0.3 mm and a        diameter of 4 mm, which was an accessory to the analysis        equipment, and a flat portion of the surface was subjected to a        measurement.

The aluminum density X1 and the fluorine density X2 in the outermostsurface layer of the toner sample were measured by X-ray photoelectronspectroscopy (XPS) using the above-described instruments under theabove-described measurement conditions, and the ratio X1/X2 wascalculated. The results are presented in Table 1.

Measurement of Peak Intensity Ratio (W/R)

The peak intensity ratio (W/R) was determined from an absorbancespectrum obtained by an ATR method (total reflection method) using anFT-IR (Fourier transform infrared spectrophotometer AVATAR 370manufactured by Thermo Electron Corporation), in which the heights ofpeaks specific to the release agent (wax) and the binder resin,respectively, were defined as W and R. Since the ATR method requires asmooth surface, the toner was pressure-molded to form a smooth surface.Specifically, 2.0 g of toner was pressure-molded with a load of 1 t for60 seconds and formed into a pellet having a diameter of 20 mm.

The maximum height of a peak specific to C—H stretching of an alkylchain of the wax (e.g., a peak observed at 2834 to 2862 cm⁻¹) wasdefined as W, and the maximum height of a peak specific to the binderresin (e.g., a peak observed at 784 to 889 cm⁻¹ for a polyester resin(see FIG. 1), a peak observed at 670 to 714 cm⁻¹ for a styrene-acrylicresin) was defined as R, and W/R was calculated as the peak intensityratio. When the binder resin is a mixture of two or more types of resinsand two or more peaks were detected, the highest peak was adopted. Thetoner of each Example contains a polyester resin and a styrene-acryliccopolymer resin, with the amount of the polyester resin greater and thepeak thereof higher. Therefore, a peak specific to the polyester resinwas adopted for the calculation.

The spectrum was converted so that the height of peak indicatedabsorbance. The peak intensity ratio (W/R) was calculated usingabsorbance values that indicated the height of peak.

Preparation of Developer

Each toner in an amount of 5% by mass was mixed with asilicone-resin-coated copper-zinc ferrite carrier having an averageparticle diameter of 40 μm in an amount of 95% by mass to prepare eachtwo-component developer.

Image Evaluation

Each two-component developer was loaded in a modified machine of acopier (IMAGIO MF7070 manufactured by Ricoh Co., Ltd.) to develop imageson 5,000 sheets per day in a low-temperature low-humidity environment(at a temperature of 10 degrees C. and a relative humidity of 15%). Inthe initial stage and after 100K (100,000) sheets were output, a whitesolid image and a black solid image were respectively printed on threeA3-size sheets (brand: RICOH MyPaper), and visually observed todetermine whether fogging had occurred. The degree of fogging wasevaluated based on the following evaluation criteria. The image density(ID) of the solid image was measured by X-Rite 938 (manufactured byX-Rite Inc.) and evaluated based on the following evaluation criteria.The results are presented in Table 1.

Evaluation Criteria for Fogging (Background Stains)

A: No fogging occurred. Very good.

B: Almost no fogging occurred. Good.

C: Slight fogging occurred. Acceptable.

D: Fogging occurred. Poor.

Evaluation Criteria for Image Density

A: Image density (ID) is 1.40 or more.

B: Image density (ID) is 1.20 or more and less than 1.40.

C: Image density (ID) is 1.00 or more and less than 1.20.

D: Image density (ID) is less than 1.00.

Evaluation Criteria for Wear of Photoconductor

A: The amount of wear of photoconductor is significantly less than thespecified value. (Good)

B: The amount of wear of photoconductor is equal to the specified value.

C: The amount of wear of photoconductor exceeds the specified value.

D: The amount of wear of photoconductor greatly exceeds the specifiedvalue.

Overall Evaluation

A: Meets and greatly exceeds the standard.

B: Meets and exceeds the standard.

C: Meets the standard.

D: Does not meet the standard at all.

TABLE 1 Image Types of External Ratio Background Density Wear of OverallAdditive Particles X1/X2 (W/R) Stains (ID) Photoconductor EvaluationExample 1 Pseudoboehmite 2.7 0.05 B B A B Example 2 Pseudoboehmite 2.70.14 A A A A Example 3 Pseudoboehmite 5.5 0.05 B B A B Example 4Pscudobochmite 5.5 0.14 B A A B Example 5 Pseudoboehmite 2.7 0.05 A B BB Example 6 Pseudoboehmite 2.7 0.14 B A B B Example 7 Pseudoboehmite 5.50.05 B B B B Example 8 Pseudoboehmite 5.5 0.14 A A B A Example 9Pseudoboehmite 2.7 0.05 A B B B Example 10 Pseudoboehmite 2.7 0.14 B A BB Example 11 Pseudoboehmite 5.5 0.05 B B B B Example 12 Pseudoboehmite5.5 0.14 A A B B Example 13 Pseudoboehmite 2.7 0.05 B B C B Example 14Pseudoboehmite 2.7 0.14 B A C B Example 15 Pseudoboehmite 5.5 0.05 A B CB Example 16 Pseudoboehmite 5.5 0.14 B A C B Example 17 Amorphous 4 0.05B B B B Aluminum Hydroxide Particles Example 18 Bayerite 4 0.05 B B B BExample 19 Pseudoboehmite 5.5 0.14 C A C C Example 20 Pseudoboehmite 2.70.14 C A B C Example 21 Pseudoboehmite 2.7 0.05 C B B C Example 22Pseudoboehmite 5.5 0.05 C B C C Example 23 Pseudoboehmite 2.6 0.14 C A BC Example 24 Pseudoboehmite 5.6 0.14 C A B C Example 25 Pseudoboehmite2.7 0.04 B C B C Example 26 Pseudoboehmite 2.7 0.15 C A B C ComparativeAlumina 2.7 0.05 A B D D Example 1 Comparative Alumina 2.7 0.05 B B D DExample 2 Comparative Alumina 2.7 0.05 A B D D Example 3

It has been found that the toners of Examples are capable of producinghigh-density images while reducing wear of the surface of theelectrostatic latent image bearer and preventing generation of fogimages over time in low-temperature low-humidity environments.

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it will be obvious that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

1. A toner comprising: base particles comprising a binder resin and acolorant; and external additive particles covering the base particles,the external additive particles comprising at least one member selectedfrom the group consisting of fluorine-containing aluminum hydroxide,fluorine-containing boehmite, and fluorine-containing pseudoboehmite. 2.The toner according to claim 1, wherein the external additive particleshave a particle diameter of from 8 to 120 nm.
 3. The toner according toclaim 1, wherein an amount of the at least one member selected from thegroup consisting of fluorine-containing aluminum hydroxide,fluorine-containing boehmite, and fluorine-containing pseudoboehmite isfrom 0.5 to 2.0 parts by mass based on 100 parts by mass of the baseparticles.
 4. The toner according to claim 1, wherein the tonersatisfies the following formula:2.7≤X1/X2 (atomic percent)≤5.8 where X1 and X2 represent an aluminumdensity and a fluorine density, respectively, as determined by X-rayphotoelectron spectroscopy.
 5. The toner according to claim 1, whereinthe base particles further comprise a release agent, wherein the tonersatisfies the following formula:0.05≤W/R≤0.14 where W and R represent heights of peaks specific to therelease agent and the binder resin, respectively, as measured by anattenuated total reflection method using a Fourier transform infraredspectrometer.
 6. A toner accommodating unit comprising: a container; andthe toner according to claim 1 accommodated in the container.
 7. Adeveloper comprising: the toner according to claim 1; and a carrier. 8.A developing device that develops an electrostatic latent image into avisible image, comprising: a developer container containing thedeveloper according to claim 7; and a developer bearer configured tobear and convey the developer or the toner.
 9. A process cartridgedetachably mountable on an image forming apparatus, comprising: anelectrostatic latent image bearer configured to bear an electrostaticlatent image; and the developing device according to claim
 8. 10. Animage forming apparatus comprising: an electrostatic latent imagebearer; a charger configured to charge a surface of the electrostaticlatent image bearer; an irradiator configured to irradiate the chargedsurface of the electrostatic latent image bearer to from anelectrostatic latent image thereon; the developing device according toclaim 8 configured to develop the electrostatic latent image with thedeveloper to form a visible image; and a transfer device configured totransfer the visible image onto a recording medium.
 11. An image formingmethod comprising: charging a surface of an electrostatic latent imagebearer; irradiating the charged surface of the electrostatic latentimage bearer to form an electrostatic latent image thereon; developingthe electrostatic latent image with the developer according to claim 7to form a visible image; and transferring the visible image onto arecording medium.